Hi Camillitech,
What is the head and flowrate of the installation and has he figured out which turbine he is going for?
Is he going hire a friction welding machine for jointing the 4" pipe lengths?
DTL
Morning DTL,
The flow is extremely variable but the head is 32m I think, and the turbine is a custom built cross flow one. The pipe is 10" and he got a fusion welder off eBay for buttons, in fact he got two

When I was looking for one last year they were like rocking horse pooh but apparently they now have to be 'certified' or something for doing utility work and few of the older ones are. The 4" pipe is mine and I used compression fittings, not too bad as they were in 80m lengths and only 11GBP each. However if I have any more issues with 'vacuum' leaks I'll weld some.
Cheers, Paul